1. Field of the Invention
The present invention relates to a zoom lens barrel in a camera.
2. Description of the Related Art
A zoom lens usually has more than one group of lenses (front and rear groups of lenses) which are moved in the optical axis direction for the zooming operation.
A drive mechanism for the zoom lens usually includes a rotatable cam ring which is provided with cam grooves for the respective lens groups, and cam pins which are provided on the lens groups to be fitted in the associated cam grooves so that the cam pins move linearly. However, in such a conventional mechanism, since each of the lens groups is engaged by the cam ring through two or three cam pins at the most, the resistance to an external shock or impact which may be applied to the lens groups is insufficient. In particular, for instance, when a shock is applied to the first (frontmost) lens group which projects outwardly from the camera body due to an accidental drop of the camera, there is a possibility that the associated cam pins of the first lens group could be broken.
It is also known to provide a cam ring with bottomed inner cam grooves. In this known lens driving mechanism, there is a possibility that light might leak from the inner periphery of the cam ring. This requires a special, expensive light intercepting mechanism.
To solve the problems mentioned above, a zoom lens driving mechanism is also known in which only the first lens group which tends to be subject to an external shock or impact is moved by a helicoid rather than a combination of the cam pins and the cam grooves. However, in a zoom lens driving mechanism using the helicoid, since the lens group(s) other than the first lens group are (is) moved by a separate cam ring, the number of components of the lens driving mechanism increases, thus resulting in a heavier, more complicated and more expensive camera.